In the prior art, in the case of a rotary electric machine having a polyphase winding and field winding and for which an AC output current from the polyphase winding is rectified by a plurality of rectifier elements or switching elements, the energization interval of the field winding of the rotor is changed in each of respective fixed periods. The proportion of the energization interval is referred to as the duty value of the field winding, which is set variably in accordance with the amount of electric power, etc., required from the rotary electric machine.
A control apparatus for a rotary machine is described in PTL 1 for use in varying the duty value of the field winding. With the control apparatus described in PTL 1, changeover can be performed between short-time rated operation in which the duty value is large, and continuous rated operation in which the duty value is small. In addition, a temperature sensor is provided close to a power transistor that controls the energizing of the field winding If the temperature detected by the temperature sensor indicates an overheated condition, then short-time rated operation is inhibited.